Electroconductive contact unit

ABSTRACT

In the electroconductive contact unit of the present invention, a gold plated layer  8  is formed over the surface of an electroconductive needle member  2  via a Ni under layer  7   a , and a layer of iridium (titanium nitride, rhodium or hafnium nitride) is formed on the gold plated layer  8  of the needle portion  2   a  by sputtering, via an Ni under layer  7   b . Thereby, the tip portion is provided with an improved resistance to oxidization and wear without using any special material for the needle member, and the durability of the needle member is improved so that the running cost can be minimized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Application of PCT InternationalApplication No. PCT/JP02/06647, International Filing Date Jul. 1, 2002,claiming priority of Japanese Patent Application JP 2001-210262, filed02 Jul. 2001.

TECHNICAL FIELD

The present invention relates to an electroconductive contact unit forexchanging signals with printed circuit boards, electronic devices orthe likes.

BACKGROUND OF THE INVENTION

A conventional electroconductive contact unit for use in contact probesfor electrically testing conductor patterns of printed circuit boardsand electronic devices typically comprises an electroconductive needlemember and a tubular holder that receives the needle member in anaxially moveable manner, and the needle member is resiliently urged by acoil spring in the direction to project the tip of the needle memberfrom the front end of the holder so that the tip of the needle membermay be resiliently brought into contact with an object to be tested.

Silicon wafers and ceramic packages for use with semiconductor devicesand glass panels for use in LCD panels are made of materials having arelatively high hardness. These components are provided with electriccircuitry, and are subjected to electric testing during themanufacturing process. An electroconductive contact unit (contact probe)is used for such a purpose, and is adapted to establish electric contactwith a part of the circuitry such as a terminal.

When the object to be tested consists of a component made of a hardmaterial such as those mentioned earlier, and the contact probe usesneedle members made of conventional SK material (carbon tool steel),repeated use of the needle members will result in the wear anddeformation of the contact points in time. As a result, a stable contactresistance may eventually become impossible. Therefore, the needlemembers are required to be replaced in a relatively short period oftime, and this increases the running cost.

SUMMARY OF THE INVENTION

In view of such problems of the prior art and to provide anelectroconductive contact unit which is resistant to wear and highlydurable, the electroconductive contact unit of the present inventionincludes an electroconductive needle member, and a coil springresiliently urging the needle member in a direction to bring a tipportion of the needle member into contact with an object to becontacted, and is characterized by that: the tip portion of the needlemember is integrally formed with electroconductive material resistant tooxidization and wear.

Thereby, the tip portion of the needle member can be made resistant tooxidization and wear, and is prevented from being worn or deformed evenwhen the object to be tested consists of material having a highhardness. Thus, the wear resistance and durability of the needle memberis improved, and a stable contact resistance is ensured.

In particular, by forming a plating of a highly electroconductivematerial at least on the remaining part of the needle member which isnot integrally formed with the electroconductive material, even when theelectroconductive material does not have an adequately highelectroconductivity owing to a greater weight placed on increasedresistance to oxidization and wear, the electric path between the tipportion of the needle member and the part thereof connected to the coilspring can be plated with highly electroconductive material so that theelectric resistance of the electric path between the needle member andcoil spring can be minimized.

The electroconductive material may consist of any of iridium, titaniumnitride, rhodium and hafnium nitride either by itself or as an alloywith gold or platinum. The favorable properties of iridium, titaniumnitride, rhodium and hafnium nitride such as a high hardness, resistanceto heat and acid and stable contact resistance can be fully takenadvantage of so that the tip portion of the needle member is given withan improved wear resistance and durability, and a favorable conductivestate (such as a stable contact resistance) can be achieved owing to thestable mechanical contact.

If the iridium, titanium nitride, rhodium, hafnium nitride or alloy ofany one of them with gold or platinum is provided via an under layer forpreventing peeling, the under layer ensures a secure attachment of suchmaterial to the needle member even when a direct application of suchmaterial to the needle member would fail to provide an adequate force ofattachment. Therefore, the electroconductive unit can be given with adesired wear resistance and durability.

By using gold for the highly electroconductive material that is plated,even when the electroconductive material does not have an adequatelyhigh electroconductivity because of a greater weight placed on increasedresistance to oxidization and wear, the needle member may be given witha high electroconductivity as a whole.

If the gold plating is formed over the entire surface of the needlemember, and the iridium, titanium nitride, rhodium, hafnium nitride oralloy of any one of them with gold or platinum is provided via an underlayer for preventing peeling, the gold plating that is provided over theentire surface of the needle member ensures a high electroconductivityfor the needle member as whole, and the under layer ensures a strongattachment of the material such as iridium to the needle member. Also,the gold plated layer under the material such as iridium conductselectricity, and provides an even more favorable electric property.

If a gold plating is formed on the outer surface of the iridium,titanium nitride, rhodium, hafnium nitride or alloy of any one of themwith gold or platinum, the material such as iridium improves the wearresistance, and the gold plated layer reduces the electric resistance ofthe needle member as a whole. Even when the gold plated layer is worn ordeformed and the under layer made of such material as iridium isexposed, the presence of the gold plated layer adjacent to such anexposed part helps the electric conductivity of the needle member to bekept high as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

Now the present invention is described in the following with referenceto the appended drawings, in which:

FIG. 1 is a vertical sectional view of an electroconductive contact unitfor use in a contact probe embodying the present invention;

FIG. 2 is a view similar to FIG. 1 showing the contact unit brought intocontact with an object;

FIG. 3 is an enlarged fragmentary sectional view of the needle memberhaving an iridium layer coated thereon;

FIG. 4 is a schematic view showing how the sputtering process isconducted;

FIGS. 5 a, 5 b and 5 c are enlarged fragmentary views showing differentshapes of the tip of a needle member;

FIG. 6 is a view similar to FIG. 3 showing another embodiment of thepresent invention; and

FIG. 7 is a view similar to FIG. 3 showing yet another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described in thefollowing with reference to the appended drawings.

FIG. 1 is a vertical sectional view showing an electroconductive contactunit 1 for use in a contact probe embodying the present invention. Thiselectroconductive contact unit 1 may be used by itself, but isparticularly suitable for use in a holder (probe head) of a multipointcontact probe as one of a large number of similar electroconductivecontact units that are arranged one next to another, for instance for awafer level test. In such a contact probe, the holder is integrallyattached to a board mounted on a testing machine via a relay circuitboard. The drawing is for illustration purpose only, and the actualaspect ratio may differ from that of the illustrated example.

The electroconductive contact unit 1 comprises an electroconductiveneedle member 2, a compression coil spring 3 and a holder 4 made ofelectrically insulating material and defining a large diameter holderhole 4 a and a small diameter holder hole 4 b in a coaxial relationshipfor receiving the electroconductive needle member 2 and compression coilspring 3 therein. The electroconductive needle member 2 comprises aneedle portion 2 a having a pointed end, a flange portion 2 b providedin the rear end of the needle portion 2 a and having a more enlargeddiameter than the needle portion 2 a, and a stem portion 2 c projectingfrom the other end (the lower end in the drawing) of the flange portion2 b and having a more reduced diameter than the flange portion 2 b.These portions 2 a, 2 b and 2 c are each provided with a circular crosssection, and disposed in a mutually coaxial relationship.

The part of the stem portion 2 c of the electroconductive needle member2 adjacent to the flange portion 2 b is formed as an enlarged diameterportion 2 d having a slightly larger diameter than the rest of the stemportion 2 c. The enlarged diameter portion 2 d is press fitted into anend of the compression coil spring 3, and the corresponding coil endthereby resiliently wraps around the enlarged diameter portion 2 d. Theelectroconductive needle member 2 is connected to the compression coilspring 3 in this manner. The connection between the enlarged diameterportion 2 d and the corresponding end of the compression coil spring 3can be accomplished not only by the resilient wrapping described abovebut also by other means such as soldering. In regard to how thecompression coil spring 3 is wound, the one end portion connected to theenlarged diameter portion 2 d consists of a closely wound portion, andthe intermediate portion consists of a coarsely wound portion while theother coil end portion is provided with a closely wound portion 3 ahaving a prescribed length.

The small diameter holder hole 4 b of the holder 4 axially slidablyreceives the cylindrical portion of the needle portion 2 a, and thelarge diameter holder hole 4 a receives the flange portion 2 b, enlargeddiameter portion 2 d, stem portion 2 c and compression coil spring 3.The lower surface of the holder 4 in the drawing is attached to a relaycircuit board 5 which closes the open end of the large diameter holderhole 4 a. The relay circuit board 5 is fixedly attached to the holder 4by threaded bolts not shown in the drawing, and is provided with aninternal circuitry 5 a having a terminal surface opposing the largediameter holder hole 4 a.

As shown in the drawing, when the holder 4 and relay circuit board 5 areassembled to each other, the electroconductive needle member 2 isprevented from coming off from the holder hole by the flange portion 2 bbeing engaged by a shoulder 4 c defined between the small diameterholder hole 4 b and large diameter holder hole 4 a. The axial length ofthe large diameter holder hole 4 a is determined in such a manner thatthe compression coil spring 3 is subjected to a prescribed initial loadby a compressive deformation thereof. The axial lengths of the stemportion 2 c and closely wound portion 3 a are determined in such amanner that the lower end of the stem portion 2 c in the drawing engagesthe closely wound portion 3 a in the illustrated initial state (prior tothe test).

Referring to FIG. 2, by engaging the tip of the needle member 2 a ontoan object to be tested such as a pad 6 a made of Au, Cu or Al and formedon the surface of the wafer 6, an electric signal I is transmitted fromthe side of the wafer 6 to the relay circuit board 5 via the needlemember 2 and compression coil spring 3. The signal is then forwarded toa control system not shown in the drawing via a circuit board not shownin the drawing connected to the relay circuit board 5, and a desiredtest can be conducted.

In the initial state, the stem portion 2 c is in contact with theclosely wound portion 3 a, and a reliable contact between the stemportion 2 c and closely wound portion 3 a can be ensured at the time oftesting as shown in FIG. 2. The electric signal I is conducted axiallythrough the electroconductive needle member 2, and then to the closelywound portion 3 a. As can be readily appreciated, the electric signalcan flow axially through the closely wound portion 3 a of thecompression coil spring 3, instead of along a spiral path, so that theinductance of the electroconductive contact unit 1 can be effectivelyminimized.

In this electroconductive contact unit 1, as shown in FIG. 3, the entiresurface of the electroconductive needle member 2 is formed with a goldplated layer 8 via a Ni under layer 7 a, and the needle portion 2 a isadditionally formed with an iridium layer 9 via a Ni under layer 7 b ontop of the gold plated layer 8. The Ni under layer 7 a improves theattachment of the gold plated layer 8. The iridium layer 9 may consistof either iridium or an iridium alloy.

An example of the structures of the various layers is given in thefollowing. The needle member 2 including the needle portion 2 a, flangeportion 2 b, stem portion 2 c and enlarged diameter portion 2 d all in acoaxial arrangement is generally Ni plated so as to form a Ni underlayer 7 a, and is gold plated thereon to form a gold plated layer 8which is highly electroconductive and wear resistant.

As shown in FIG. 4, the electroconductive needle member 2 formed withthe gold plated layer 8 is held by a fixture 10 at the base end(adjacent to the flange portion 2 b) of the needle portion 2 a. A Niunder layer 7 b having a thickness of 1 μm or less is formed on the partof the needle portion 2 a exposed from the fixture 10, and the needleportion 2 a still held by the fixture 10 is exposed to an Ir target 11so that sputtering may be conducted thereon from above and sideways.Iridium (or an alloy thereof) which is resistant to oxidization, wearresistant and electroconductive is thus sputtered over the entiresurface of the needle portion 2 a so as to form an iridium layer 9having a thickness of approximately 0.5 μm or less. The needle portion 2a is held by the fixture 10 by clamping as illustrated in FIG. 4, butmay also by hooking the flange portion 2 b onto a fixture, and theorientation of the needle portion may also be horizontal or inverted asdesired.

Iridium was used in the illustrated embodiment, but the presentinvention is not limited by this selection of the material, and thereare other materials that can achieve a similar result such as titaniumnitride (TiN), rhodium (Rh) and hafnium nitride (HfN). A titaniumnitride layer can be formed simply by replacing the iridium target ofthe foregoing embodiment with a titanium nitride target. Rhodium may beused as a layer of an alloy of platinum and rhodium formed by sputteringa mixture of platinum and rhodium

In regard to titanium nitride, by sputtering both titanium nitride andgold or platinum in a nitrogen environment, a layer of an alloy oftitanium nitride and gold or platinum can formed. Similarly, in regardto hafnium nitride, by sputtering both hafnium nitride and gold orplatinum in a nitrogen environment, a layer of an alloy of hafniumnitride and gold or platinum can formed. The rhodium, titanium nitrideand hafnium nitride layers that can be used in place of the iridiumlayer 9 can provide a similar performance, and the tip of the needlemember 2 can be made electroconductive, resistant to oxidization andwear resistant.

According to this arrangement, it is possible to benefit from theadvantages of such materials as iridium, titanium nitride, rhodium andhafnium nitride. The advantages include high hardness, resistance toheat and acid, and a stable contact resistance. In particular, the wearresistance and durability of the tip of the needle portion 2 a can beimproved, and a conductance based on a highly stable mechanical contactcan be ensured (the contact resistance can be made stable). Because thealloy layer or metallic layer can be formed by plating or sputtering,the advantages of the present invention can be gained without modifyingthe existing shape of the electroconductive needle member, and thisprevents a rise in the manufacturing cost.

Because only the part that may wear or deform due to impacts andpressure is required to be processed for an increased hardness (such asthe formation of an iridium layer in the foregoing embodiment), theremaining part of the needle member may be coated with a highlyelectroconductive material such as a gold plated layer. For instance,because the enlarged diameter portion which is press fitted into thecompression coil spring is provided with a gold plated layer 8, thecontact resistance between the press fitted part of the compression coilspring and the needle member can be minimized. Therefore, even when apart of the electric signal I flows via the press fitted part of thecompression coil spring 3, the influence from the resulting contactresistance can be minimized.

FIG. 2 shows the way the electric signal I flows, and it can be seenthat the electric signal I flows through the contact portion between thestem portion 2 c of the needle member 2 and the closely wound portion 3a of the coil spring 3. In this case, the electric signal flows throughthe needle member 2 mostly via the gold plated layer 8 owing to the skineffect. The electric signal may be conducted by the iridium layer 9 atthe tip of the needle portion 2 a, but because the gold plated layer 8is formed in the lower layer of the needle portion 2 a the electricsignal also flows through the gold plated layer 8. In this manner,having the gold plated layer 8 formed over the entire surface of theneedle member 2 produces a highly desirable result. Also, the goldplated layer 8 on the stem portion 2 c is beneficial when soldering thecoil spring 3 thereto. The gold plated layer 8 ensures the corrosionresistance of the needle member 2, and allows the material of the needlemember 2 to be selected relatively freely without regard to theelectroconductivity or corrosion resistance thereof.

The Ni under layer 7 b was formed before forming the iridium layer 9because iridium is resistant to oxidization and wear andelectroconductive but cannot be coated directly over the gold platedlayer 8 without difficulty. By the intervention of the Ni under layer 7,the coating strength (resistance to peeling) of iridium can besignificantly improved. The material for this under layer 7 is notlimited to Ni, but may also be others as long as they can improve theresistance of iridium against peeling.

When the iridium layer 9 was formed on the surface of the tip of theneedle member 2, the diameter of the tip was approximately 5 μm or lessafter it was applied to a glass plate one million times and the wear ofthe iridium layer 9 was relatively insignificant. When the needle memberwas only coated with a gold plated layer, the diameter of the tip wasapproximately 20 μm or more after it was applied to a glass plate onemillion times and the underlying metal was exposed.

The tip of the needle portion 2 a was provided with a pointed conicalshape in the illustrated embodiment, but the shape is not limited bythis example. For instance, the tip may be formed as any of thoseillustrated in FIGS. 5 a to 5 c. The one illustrated in FIG. 5 a has aconical shape having a rounded tip. The one illustrated in FIG. 5 b isshaped as a combination of a plurality of prismatic shapes. The oneillustrated in FIG. 5 c is provided with a blunt and flat end surface.The shape of the tip can be suitably selected according to the shape ofthe object to be contacted. For instance, the one illustrated in FIG. 5c is suitable for contact with a solder ball.

Furthermore, by orienting the sputtering direction as represented byarrow S in FIG. 5 a, the iridium layer may be formed only on each of thefaces 12 a, 12 b and 12 c (tip of the needle member) directed toward thesputtering direction. In such a case, the iridium layer is formed onlyon the surface that is to be contacted with an object to be contacted,and the material cost can be minimized.

In the foregoing embodiment, the electroconductive contact unit had onlyone end that is moveable. However, the present invention can be appliedto electroconductive contact units having two moveable ends, and thoseusing an electroconductive needle member that is supported as acantilever. In such a case, it suffices if at least the tip (the partthat comes into contact with the object to be contacted) of the needlemember is integrally provided with material which is resistant tooxidization and wear and electroconductive such as iridium.

As illustrated in FIG. 6, an additional gold plated layer 13 may beformed on the surface of the iridium layer 9. In this arrangement, theiridium layer 9 provides the required resistance to wear and the goldplated layer 13 provides the corrosion resistance and low electricresistance, and an needle member providing an even more stable contactresistance can be achieved. Even when the gold plated layer 13 has wornout or deformed and the underlying iridium layer 9 is exposed, owing tothe gold plated layer 13 still remaining around the exposed portion, ahigh electric conductivity of the needle member 2 can be maintained as awhole.

In the illustrated embodiments, the gold plated layer 8 was formed overthe entire surface of the needle member 2, and the iridium layer 9 wasformed only on the tip of the needle member 2 on top of the gold platedlayer 8, but the gold plated layer 8 may be omitted from the part wherethe iridium layer 9 is formed. In other words, the gold plated layer isrequired to be provided at least in the part (such as the flange portion2 b, enlarged diameter portion 2 d and stem portion 2 c in the case ofthe illustrated embodiments) where the iridium layer 9 is not formed.

FIG. 7 illustrates such an example. The embodiment illustrated in FIG. 7is similar to that illustrated in FIG. 3, and the corresponding partsthereof are denoted with like numerals without repeating the descriptionof such parts. As shown in the drawing, a Ni under layer 7 a is providedover the entire surface of the needle member 2, and an iridium layer 9is formed on the needle portion 2 a. The part where the iridium layer 9is absent (the flange portion 2 b, enlarged diameter portion 2 d andstem portion 2 c in the case of the illustrated embodiments) is formedwith a gold plated layer 8. The order of forming these two layers 8 and9 can be freely selected, and a mask may be used when forming eachlayer. In the case of the embodiment illustrated in FIG. 7, the electricsignal flows first through the iridium layer 9 and then through the goldplated layer 8. When this is applied to the embodiment illustrated inFIG. 6, the electric signal can transmit from the gold plated layer 13to the gold plated layer 8, and the favorable electric properties ofgold can be even more fully taken advantage of.

Although the present invention has been described in terms of preferredembodiments thereof, it is obvious to a person skilled in the art thatvarious alterations and modifications are possible without departingfrom the scope of the present invention which is set forth in theappended claims.

INDUSTRIAL APPLICABILITY

As can be appreciated from the foregoing embodiments, the tip of theneedle member can be made highly resistant to oxidization and wear, andthe wear resistance and durability of the electroconductive contact unitcan be improved easily without using any special material for the needlemember. For instance, even when material such as iridium not having afavorable electric conductance is used, the resistance of the electricpath between the needle member and coil spring can be minimized byplating at least the remaining part of the needle member with materialhaving a high electric conductivity. Therefore, the durability of theneedle member is improved, and the running cost can be reduced.

In particular, by forming a gold plated layer over the entire surface ofthe needle member, and additionally forming a layer consisting of any ofiridium, titanium nitride, rhodium and hafnium nitride either by itselfor as an alloy with gold or platinum via an under layer for preventingpeeling, even when the needle member is made of conventionally usedmaterial such as SK material, the gold plated layer reduces the electricresistance of the electric path extending from the tip of the needlemember to the coil spring, and the under layer permits the material suchas iridium to be firmly attached to the gold plated layer. Thereby, thefavorable properties of the material such as iridium can be given to theneedle member. The favorable properties include high hardness,resistance to heat and acid and a stable contact resistance. The goldplated layer provides a high electric conductivity in a stable manner.

By forming a gold plated layer on top of the layer of material such asiridium, the wear resistance can be increased owing to the material suchas iridium, and a low electric resistance can be ensured owing to thegold plated layer at the same time. In such a case, even when the goldplated layer is worn or deformed and the underlying layer made of suchmaterial as iridium is exposed, the presence of the gold plated layeradjacent to such an exposed part helps the electric conductivity of theneedle member as a whole to be kept high.

1. An electroconductive contact unit, comprising: a holder member havinga large diameter holder hole and a small diameter holder hole; anelectroconductive needle member including at least a needle portionformed at an axial end thereof protruding through the small diameterholder hole and a stem portion formed at an opposite axial end thereofreceived by the large diameter holder hole; and a coil spring coaxiallysurrounding the stem portion and including at least a first end engagedwith a part of the stem portion of the needle member and a second endfixed in relation to the holder member and electrically connected to acircuit board, the coil spring resiliently urging the needle member in adirection to bring the needle portion of the needle member into contactwith an object to be contacted and providing an electroconductive pathbetween the needle member and the circuit board, wherein, at least a tipportion of the needle portion of the needle member is formed with alayer of electroconductive material resistant to oxidization or wearcomprising iridium, titanium nitride, rhodium or hafnium nitride eitherby itself or as an alloy with gold or platinum, or a combinationthereof, and at least a part of the stem portion of the needle membercomprises a plated layer of highly electroconductive material.
 2. Anelectroconductive contact unit according to claim 1, wherein the layerof the electroconductive material resistant to oxidization and wear isformed via an under layer for preventing peeling.
 3. Anelectroconductive contact unit according to claim 2, wherein the underlayer comprises nickel.
 4. An electroconductive contact unit accordingto claim 1, wherein the highly electroconductive material of the platedlayer comprises gold.
 5. An electroconductive contact unit according toclaim 4, wherein the plated layer of gold is formed via an under layer.6. An electroconductive contact unit according to claim 5, wherein theunder layer comprises nickel.
 7. An electroconductive contact unitaccording to claim 1, wherein the needle member comprises a flangebetween the needle portion and stem portion thereof to engage the firstend of the coil spring, the first end of the coil spring and stemportion engaging each other via the plated layer of the highlyelectroconductive material.
 8. An electroconductive contact unitaccording to claim 1, wherein the coil spring includes a closely wouldportion at which a rear end of the stem portion engages, the rear end ofthe stem portion being formed with the plated layer of the highlyelectroconductive material.
 9. An electroconductive contact untiaccording to claim 1, wherein the plated layer of the highlyelectroconductive material substantially covers the needle member, andthe layer of the electroconductive material resistant to oxidization andwear covers only the needle portion of the needle member.
 10. Anelectroconductive contact unit according to claim 9, comprising anadditional plated layer of gold formed over the layer of theelectroconductive material resistant to oxidization and wear.
 11. Anelectroconductive contact unit according to claim 1, wherein the platedlayer of the highly electroconductive material covers only the stemportion of the needle member, and the layer of the electroconductivematerial resistant to oxidization and wear covers only the needleportion of the needle member.